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Monkeyface is a slang term for a sexual technique focused on degradation of the victim (see Donkeypunch). The technique is usually performed by a male on a female, and as such has strong misogynist overtones. Like other terms of its kind, the main function of the term is to get shock value and humor through describing the technique to others.
The technique involves the man first completely shaving his pubic hair and placing it all where it can be easily reached, e.g. a bedside table. The man then has his woman perform fellatio on him to completion. As the man ejaculates, he attempts to coat the woman's face with his semen. Upon finishing, the man then grabs all of his loose pubic hair, throws it so that it sticks to the woman's face, and then points and yells, "Monkeyface!"